Ferroelectric and piezoelectric properties of blends of poly(vinylidene fluoride-trifluoroethylene) and a graft elastomer

A piezoelectric polymeric blend system has been developed. The system contains two components: ferroelectric poly(vinylidene fluoride-trifluoroethylene) and graft elastomer. The remanent polarization, P_r, and the piezoelectric strain coefficient, d₃₁, of the blends have been studied as a function of relative composition of the two components, temperature and frequency. Both blended copolymer and graft unit in the elastomer contribute to the total crystallinity of the blend-system, and hence to the remanent polarization and piezoelectricity. The piezoelectric strain coefficient, d₃₁, of the blend systems shows dependence on both the remanent polarization and the mechanical stiffness, which in turn are determined by the fraction of the two components in the blends. This mechanism makes it possible for the piezoelectric strain response of the blend to be tailored by adjusting the relative composition. Although P_r of the copolymer is higher than that of the blends, the blend films containing 75 wt.% copolymer exhibit a higher d₃₁ at room temperature, possibly due to their lower modulus. The blend films containing 50 wt.% copolymer exhibit a constant value of d₃₁, from room temperature to 70°C.